Cabazitaxel, (αR,βS)-α-hydroxy-β-[[(1,1-dimethylethoxy)carbonyl]amino]-benzenepropanoic acid (2aR,4S,4aS,6R,9S,11S,12S,12aR,12bS)-12b-(acetyloxy)-12-(benzoyloxy)-2a,3,4,4a,5,6,9,10,11,12,12a,12b-dodecahydro-11-hydroxy-4,6-dimethoxy-4a,8,13,13-tetramethyl-5-oxo-7,11-methano-1H-cyclodeca[3,4]benz[1,2-b]oxet-9-yl ester, has the following chemical structure:

Cabazitaxel is a semi-synthetic taxoid derivative. It is marketed under the trade name JEVTANA® for the treatment of hormone-refractory prostate cancer.
Cabazitaxel and a process for its preparation are disclosed in U.S. Pat. No. 5,847,170. Cabazitaxel acetone solvate is disclosed in U.S. Pat. No. 7,241,907. Several solid state forms of Cabazitaxel are disclosed in WO 2009/115655.
Polymorphism, the occurrence of different crystal forms, is a property of some molecules and molecular complexes. A single molecule, like Cabazitaxel, may give rise to a variety of polymorphs having distinct crystal structures and physical properties like melting point, thermal behaviors (e.g. measured by thermogravimetric analysis—“TGA”, or differential scanning calorimetry—“DSC”), powder X-ray diffraction (PXRD) pattern, infrared absorption fingerprint, and solid state NMR spectrum. One or more of these techniques may be used to distinguish different polymorphic forms of a compound.
Discovering new polymorphic forms and solvates of a pharmaceutical product can provide materials having desirable processing properties, such as ease of handling, ease of processing, storage stability, and ease of purification or as desirable intermediate crystal forms that facilitate conversion to other polymorphic finals. New polymorphic forms and solvates of a pharmaceutically useful compound or salts thereof can also provide an opportunity to improve the performance characteristics of a pharmaceutical product. It enlarges the repertoire of materials that a formulation scientist has available for formulation optimization, for example by providing a product with different properties, e.g., better processing or handling characteristics, improved dissolution profile, or improved shelf-life.